The pneumatic riveting hammer is an intensive source of vibration due to the impact principle of operation.
By transmitting substantial vibration over a wide frequency range to the operator's hands, the hammer causes considerable changes in the bone-muscular, vessel and nervous systems. The complex of these changes is referred to as a "vibration disease" which is one of the most serious occupational diseases.
The investigation of the causes of the disease has made it possible to determine the criteria of the vibration action and to find out the permissible levels of vibration to which the operator is subjected during the working shift.
These criteria are the values of the average square vibration velocity in the octave frequency bands over a range of 11 to 2800 Hz, being different for each octave band.
In this connection the vibration of any power tool acting on the operator's hands must be within the permissible levels, i.e. any hand-held power tool, a riveting hammer in particular, must be periodically checked for vibration safety with a view to rejecting the tools which do not meet said requirements.
Known in the art is a substantially large number of means for measuring and analyzing vibration in the required frequency range. However, the methods of taking measurements on riveting hammers do not ensure true and objective results. The main method of testing riveting hammers for vibration safety is to measure their vibration parameters directly during the riveting work carried out by the operators. The drawback to this method is the subjectivity of the vibration measurements since the magnitude and nature of riveting hammer vibration substantially depend on physiological characteristics of the operator, the pressure exerted by him on the riveting hammer, the grasping force, and the methods of operation. The "vibration disease" is much more likely to develop in the operators who test riveting hammers than in the operators who work with riveting hammers that have passed the vibration safety test. Moreover, the testing of riveting hammers through the use of riveting operators is carried out at a low rate of work.
A more progressive method of testing hand-held riveting hammers is to use test benches without recourse to riveting operators. The test-bench conditions provide for a fairly higher rate of testing work and, above all, provide for objective vibration measurement unbiased by operators' individual characteristics. However, the prior-art benches for testing riveting hammers were devised before the establishment of the present health care limitations on vibration and, therefore, their design does not provide for the operatng range of hammer vibration in the frequency range involved.
Known in the art is a vibration safety test bench for hand-held riveting hammers (refer to USSR Inventor's Certificate No. 189609, class G01M 15/00) which comprises a bed with a dummy work rigidly secured thereto, a mounting for a hand-held riveting hammer under test and a mounting for a dolly, said mountings being located at either side of said dummy work and adapted to be moved along said bed, and a vibration pickup designed to sense the vibration of the hand-held riveting hammer being tested and connected to a vibration metering device. The vibration of the riveting hammer is measured on this test bench by means of a vibrograph capable of registering the amplitude of hammer vibration at the frequency of hammer blows, i.e. within 100 Hz. The riveting hammer under test and the dolly are rigidly secured in the mountings which ignore the influence of the operator's hands on the vibration of the hammer and dolly.
During the operation of the riveting hammer under test its vibration is transmitted to the mountings the mass of which becomes added to that of the hammer, the vibration of the hammer handle being thereby substantially distorted.
It follows that the test bench under consideration does not provide the true operating conditions of the hammer under test and the measurements obtained do not correspond with the actual vibration acting on the operator's organism.